Stroke places a serious health burden on our society in terms of mortality, morbidity, and economic cost. Leukocyte-mediated inflammation is known to damage the brain several hours to days following stroke. However, it is unclear whether leukocytes accumulate and cause injury when blood is first returned to the brain. Therefore, the specific aims of this proposal are to 1) identify the exact locations of leukocyte accumulation in the rat cerebral microcirculation during the first 60 minutes of reperfusion following stroke using the clinically relevant model of stroke, middle cerebral artery occlusion, and in-vivo video microscopy 2) examine the contribution of the cytokine, interleukin-1 (IL-1) to early leukocyte retention by measuring the levels of IL-1 in brain and peripheral blood, by examining the effect of IL-1 on leukocyte adhesion molecule CD1b expression and oxygen radical production with flow cytometric techniques, and by pretreating animals with stroke with an IL-1 receptor antagonist and 3) examine the functional significance of leukocyte accumulation in the cerebral microcirculation during early reperfusion following stroke by assessing brain electrical activity. This information will more clearly characterize the locations, mechanisms, and functional significance of early vascular leukocyte accumulation after stroke. This information will also aid in the development of optimal therapies for stroke and be useful in formulating nursing research questions related to the treatment of acute stroke.